feat: add View as Customer impersonation button on Clients page (#64)

Staff can now click "View as Customer" on any client profile in the admin
panel. This navigates to the customer portal with impersonation auto-activated,
showing the portal exactly as that customer would see it (read-only, with
full audit trail).

The portal reads impersonate/clientName/reason/staffName from URL search
params on mount, auto-starts the impersonation session, then cleans up the
URL.

Co-authored-by: Groom Book CTO <cto@groombook.dev>
Co-authored-by: Paperclip <noreply@paperclip.ing>

apps/web/src/pages/Clients.tsx

@@ -360,6 +360,12 @@ export function ClientsPage() {
               )}
             </div>
             <div style={{ display: "flex", gap: "0.5rem", marginLeft: "auto" }}>
+              <a
+                href={`/?impersonate=true&clientName=${encodeURIComponent(selectedClient.name)}&staffName=${encodeURIComponent("Staff")}&reason=${encodeURIComponent(`Support view for ${selectedClient.name}`)}`}
+                style={{ ...btnStyle, backgroundColor: "#fef3c7", color: "#92400e", borderColor: "#fde68a", textDecoration: "none", display: "inline-flex", alignItems: "center", gap: "0.3rem" }}
+              >
+                👁 View as Customer
+              </a>
               <button onClick={() => openEditClient(selectedClient)} style={btnStyle}>
                 Edit client
               </button>

apps/web/src/portal/CustomerPortal.tsx

@@ -1,4 +1,4 @@
-import { useState, useReducer, useCallback } from "react";
+import { useState, useReducer, useCallback, useEffect } from "react";
 import {
   Home, Calendar, PawPrint, FileText, CreditCard, MessageSquare,
   Settings, Eye, LogOut, Clock, Shield,
@@ -101,6 +101,27 @@ export function CustomerPortal() {
   const [impersonation, dispatchImpersonation] = useReducer(impersonationReducer, null);
   const { branding } = useBranding();
 
+  // Auto-start impersonation from URL params (staff flow from admin panel).
+  // Runs once on mount only — impersonation state is managed by the reducer after init.
+  const [impersonationInitDone, setImpersonationInitDone] = useState(false);
+  useEffect(() => {
+    if (impersonationInitDone) return;
+    const params = new URLSearchParams(window.location.search);
+    if (params.get("impersonate") === "true") {
+      const clientName = params.get("clientName") || "Unknown Customer";
+      const reason = params.get("reason") || `Viewing portal as ${clientName}`;
+      const staffName = params.get("staffName") || "Staff";
+      dispatchImpersonation({
+        type: "START",
+        staffName,
+        staffRole: "Admin",
+        reason,
+      });
+      window.history.replaceState({}, "", window.location.pathname);
+    }
+    setImpersonationInitDone(true);
+  }, [impersonationInitDone]);
+
   const logPageView = useCallback((page: string) => {
     if (impersonation?.active) {
       dispatchImpersonation({